1. Field of the Invention
The present invention relates to quick change chucks for power tools and, more particularly, to an improved chuck that provides increased holding force without sacrificing ease of bit changing.
2. Discussion of Related Art
Although there are a number of existing chucks and like devices for retaining cutting bits in power tools and driven spindles, they all have some disadvantages which detract from their advantages. For example, while some chucks hold the cutting bit with enough force that slippage will not occur, the changing of the bit can be very cumbersome and time consuming. Others allow an easy changing of bits but do not provide enough holding torque to prevent slippage from occurring. There are a few chucks that allow easy changing of bits and also provide a reasonable amount of holding torque. However, at the present time, there are no chucks currently available which allow an easy change of the cutting bit and which also provide the increase in mechanical advantage necessary to enable a large enough force to be exerted on the cutting bit so as to substantially increase the holding torque. A chuck of this type would allow the power tool user to spin much larger cutting bits at higher speeds while still maintaining a substantially greater safety margin because of the increased holding force.
One chuck of particular interest here is that disclosed in U.S. Pat. No. 5,096,212 to Walsh. Although this chuck has advantages, there are several disadvantages to the chuck. By way of background, it is noted that routers are required to spin the cutting bit at a relatively high angular speed, typically above 20,000 rpms. Thus, the design of a router chuck has to be as lightweight and compact as possible for obvious reasons. Accordingly, if the chuck is relatively heavy and bulky in size as in the case of the chuck of the Walsh patent, unwanted and sometimes severe vibration can occur, resulting in an unsafe operating condition. Further, the chuck of the Walsh patent requires two cams which secure the tool essentially by pinching the tool shank. Since the cams are harder than the typical tool shank, an unwanted indentation in the tool shank can result if the cams are over-tightened. Another disadvantage of the Walsh chuck is that the manner in which the nut is attached to the body is inadequate. In this regard, although during the short time a chuck constructed as disclosed in the Walsh patent was distributed no failures were reported, the construction could have eventually led to catastrophic failure. Finally, the construction of the chuck of the Walsh patent employs some unnecessary parts, includes a relatively weak screw, and, in general, has the appearance of being cumbersome and awkward to use.
An improvement in the construction of quick change router chucks and the like is disclosed in U.S. Pat. No. 6,332,619 B1 to DeRosa. The genesis of this construction was an attempt to overcome all, or as many as possible, of the shortcomings of the Walsh chuck. The attempt was successful and the construction of the DeRosa chuck not only incorporates several improvements but has been manufactured and sold in quantity to the general public. One improvement is the use of only a single cam instead of two. The single cam was also modified and is allowed to slightly crush under pressure. However, while the cam maintains its holding power, it does not indent the tool shank. The nut is attached by the use of retaining rings which are much stronger and safer than the previously used pins. Among other advantages, the size of the chuck was greatly reduced by the elimination of one cam and a few unnecessary internal parts, and a stronger screw was incorporated. However, one disadvantage is that some of the holding power provided by the chuck had to be sacrificed by the use of the softer cam in eliminating the tool shank indentation problem created by the previous use of a harder cam.